I’m taking my facts from Realclimate.org. Briefly, a re-analysis of US temperature data for the years 2000-06 reduced the mean temperature in the US in those years by 0.15%, with some smaller knock-on effects from earlier years. The effect of this was (among other things) to reduce the average temperature in the US in 1998 by 0.02 degrees, so that it is now believed to be 0.01 degrees colder than 1934, rather than 0.01 degrees hotter. The effect of this change on the analysis of global temperature is insignificant; the change was only to US temperatures.

To quote from realclimate directly:

“In the global mean, 2005 remains the warmest (as in the NCDC analysis). CRU has 1998 as the warmest year but there are differences in methodology, particularly concerning the Arctic (extrapolated in GISTEMP, not included in CRU) which is a big part of recent global warmth. No recent IPCC statements or conclusions are affected in the slightest.”

But to quote Michael Duffy:

“Imagine if the American government agency responsible for temperature records had announced a fortnight ago that it had overestimated annual temperatures since the year 2000. Imagine if, at the time of correcting this error, the hottest year on record was mysteriously altered from 1998 to 1934. “

The most egregious problem in this statement (which is the shocking statement he opens with) is that it implies that this change is a global change. In fact, it is a US one. And of course, the secondary problem with this statement, is that if you did take Michael Duffy’s US-centricity as absolutely the correct way to measure global warming, is that the change that he is trumpeting as complete proof of lack of global warming is 0.02 degrees celsius.

I’ve been trying to work out why I believe realclimate.org rather than Michael Duffy. And I think it is because realclimate.org is prepared to show some actual statistics in its (similar length) article. Whereas Michael Duffy is content with claim and counterclaim, realclimate.org is happy to show the actual data, as it has best been measured. And that is, of course, because it is written by a bunch of actual scientists, who, as a matter of habit, will hypothesise, measure, and test their hypothesis. Rather than right wing columnists, who clutch, like drowning men, at any shred of anecdote (particularly when someone in the US has already pulled together the innuendo that they can use in their column) that will enable them to ignore the weight of data that is getting more and more powerful with every passing season.

I’ll leave you with these pictures of the arctic icecap in September 1979 and August 2007 (and September usually has less ice in any given year than August) – courtesy of realclimate.org. I wonder if Michael Duffy will still be pretending that global warming doesn’t exist while sailing through the new improved Northwest passage in 10 years time?